1. Field of the Invention
The present invention relates to an image forming apparatus which stores image data of each page of a multiple page original document once into an image memory and which then outputs each of the image data stored in the image memory in order of pages of the original document to record the corresponding image on a recording medium for producing a requested number of sets of copies of the original document.
2. Discussion of the Background
A function of an image forming apparatus to store image data of each page of a multiple page original document once into a memory, and to then output the image data stored in the memory in order of pages of the original document, to record the corresponding image on a recording medium for producing a requested number of sets of copies of the original document is called electronic sorting.
Generally, for storing image data of a multiple page original document into an image memory, an image forming apparatus having an electronic sorting function reads an image of each page of the original document with an image reading device page after page and writes resulting image data into the image memory. When a writing address of the image memory exceeds a last address of the memory while storing the image data into the memory, the image forming apparatus prohibits writing the image data into the memory thereafter, and discontinues reading of the original document at the same time. Once reading of the original document is discontinued, an operator instructs the image forming apparatus to output the image data stored in the memory to record the corresponding images on recording media to produce a requested number of sets of copies of pages of the original document which have been read and stored in the memory. After the requested number of sets of copies of such pages are made, the operator instructs the image forming apparatus to restart reading of an image of each page of the original document which remains to be copied.
The image forming apparatus with the above-mentioned electronic sorting function determines if the memory will overflow, after reading an image of a page of the original document and after starting writing of the resulting image data into the memory, when the writing address exceeds the last address of the memory. Therefore, it may occur that the memory will overflow in the middle of writing image data of a certain page of the original document into the memory. In such a case, the image of that page of the original document needs to be read again since the image data of that page is not stored in the memory.
Therefore, if an operator has removed from the contact glass the page of the original document for which image data has not been stored in the memory due to a memory overflow, the operator needs to put that particular page back on the contact glass for reading the image of the page again. When an automatic document feeder is used, the sheet of the original document, which is fed out from the automatic document feeder onto the contact glass so as to be read by the reading device, has to be taken out of the contact glass and put back on the automatic document feeder again, thus causing lowering of copying productivity.
Further, there is a possibility that the operator misunderstands that the image of the page of the original document which is on the contact glass has been read and the resulting image data has been stored in the memory, even though the image data for that particular page has not been stored in the memory due to the memory overflow which occurred during storing of the image data of that page in the memory. If the operator then restarts copying of the original document from a next page of the original document, it results that the page of the image data which has not been stored in the memory due to the memory overflow during storing of the image data thereof is missed from the copies.
For preventing occurrence of missing pages as mentioned above, it is necessary to display a message, as an example, indicating that the page on the contact glass has not been read and is required to be read again, making the process of displaying messages relatively complicated.